This invention relates generally to battery power supply and, more particularly, to thermal management in such battery power supply systems. The word xe2x80x9cbatteryxe2x80x9d here is meant to include various forms of electrochemical power generation which have in common that chemical energy, in the form of one or more chemical reactants stored in a confined space, react with each other or with an external reactant in an electrochemical reaction, so as to produce electric power when desired.
Various uses of battery power supplies have been well established. For example, the packaging together of a plurality of cells in a parallel or series configuration to form a battery module or pack for use as a power supply for personal electronic devices such as cell phones, lap top computers, camcorders or the like have become well-known and common. In addition, desirable properties or characteristics of battery power supplies including, for example, the capability of certain battery power supplies to be recharged makes such battery power supplies potential power sources for vehicle propulsion, i.e., electric vehicles (EV). Recently, the concept as well as the application of battery power has been extended to include xe2x80x9cfuel batteriesxe2x80x9d or xe2x80x9cfuel cell batteriesxe2x80x9d, in which a fuel cell reaction is used to generate electric power similarly as in a conventional rechargeable battery, but in which one of the reactants (the fuel) must be replenished from time to time.
In various such applications, it is common that a number of cells be packed together in a preselected configuration (e.g., in parallel or in series) to form a battery module. A number of such battery modules may, in turn, be combined or joined to form various battery packs such as are known in the art. During operation and discharge, such cells, battery modules or battery packs commonly produce or generate quantities of heat which can significantly impact the performance resulting therefrom. Thus, in order to maintain desired or optimal performance by such cells or resulting battery modules or battery packs, it is generally important to maintain temperature of such cells, battery module or battery packs within fairly narrow prescribed ranges.
In practice, temperature variations between individual cells can result from one or more of a variety of different factors including, for example:
1) changes in ambient temperature;
2) unequal impedance distribution among cells and
3) differences in heat transfer efficiencies among cells.
Differences in heat transfer efficiencies among cells can typically primarily be attributed to the cell pack configuration. For example, cell elements at the center of a cell pack configuration may tend to accumulate heat while those cell elements at the periphery of a cell pack configuration will generally tend to be more easily or freely cooled as a result of heat transfer to the surrounding environment. Further, such variation in heat transfer efficiencies may lead to further differences in impedance such as may serve to amplify capacity differences among the cells. Such capacity imbalances can cause or result in some cells being over-charged or over-discharged which in turn may result in premature failure of the cell pack or specific cell elements thereof. In particular, such failures may take the form of thermal runaway or accelerating capacity fading.
Thermal management systems based on the use of active cooling (e.g., such as based on forced circulation of air, liquid or other selected cooling medium) have been proposed for use in conjunction with such battery power supply systems. However, the incorporation and use of such active cooling regimes may introduce a level of complexity in either or both power supply design and operation such as may hinder or prevent the more widespread use of such power supplies.
Further, the required or desired size of a battery power supply is generally dependent on the specific application thereof. Thus, certain contemplated or envisioned applications for such power supplies, such as to power electric vehicles, for example, may necessitate the use of such power supplies which have or are of significantly larger physical dimensions that those commonly used or available. As will be appreciated by those skilled in the art, thermal management in power supply systems can become even more critical or significant as the size of such cell, battery module, or battery pack is increased.
Thus, there is a need and a demand for new and improved power supply systems and methods of operation which permit either or both more efficient and effective thermal management. In particular, there is a need and a demand for such power supply systems and methods of operation which desirably avoid the potential complications and complexities of typically contemplated active cooling thermal management systems. Further, there is a need and a demand for a well designed thermal management system such as can desirably better ensure one or more of the performance, safety or capacity of an associated power supply.
A general object of the invention is to provide an improved power supply system and method of operation.
A more specific objective of the invention is to overcome one or more of the problems described above.
The general object of the invention can be attained, at least in part, through a power supply system which includes at least one cell element capable of a heat-generating charge or discharge of electric power and a supply of phase change material in thermal contact with the at least one cell element whereby the phase change material absorbs at least a portion of the heat generated upon a discharge of power from the at least one cell element.
The prior art generally fails to provide a power supply system and method of operation which provides or results in thermal management which is either or both as effective and efficient as may be desired. Further, the prior art generally fails to provide power supply system thermal management and operation such as may more conveniently or effectively permit the use of larger-sized battery power supplies such as contemplated or envisioned for certain applications, such as to power electric vehicles, for example.
The invention further comprehends a method of operating a power supply system. In accordance with one embodiment of the invention, such a method includes discharging at least one cell element to produce a quantity of power and a quantity of heat. Alternatively, the charging of at least one cell element may produce similarly a quantity of heat. At least a portion of the quantity of heat is absorbed in a phase change material in thermal contact with the discharging cell element. Such method further includes subsequently releasing at least a portion of the absorbed quantity of heat from the phase change material to heat the at least one cell element.
Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings.